1. Field of the Invention
The invention relates generally to processes for obtaining polarized articles. More particularly, certain of the articles may be optical lenses, and a polarized polyvinyl alcohol film may be used.
2. Description of Related Art
Most ophthalmic lenses sold today are plastic. During the manufacturing of a plastic lens, it is desirable to incorporate a polarizing film that will eliminate glare. Several types of polarizing films are used. One such type is polyvinyl alcohol (PVOH) that is stretched, aligning the molecules in one direction, and then dipped into iodine (see U.S. Pat. No. 2,237,567, incorporated by reference). Such films and others (see U.S. Pat. No. 6,113,811, incorporated by reference) are known to those of ordinary skill in the art. Dichroic dyes also are used, as are other film materials such as polyethylene terephthalate (PET) (see U.S. Pat. No. 6,432,327, incorporated by reference).
Typically, polarized films are treated with an adhesive material (see U.S. Pat. No. 6,220,703, incorporated by reference) and placed into a casting cell; a liquid monomer is introduced into the casting cell and the monomer is cured, encapsulating the film. Other methods also exist where the film can be directly laminated onto the front surface of a lens (U.S. Pat. No. 6,177,032, incorporated by reference), or between two lenses.
A polarizer also can be laminated onto a support or laminated between two supports. The supports are typically cellulose acetate butyrate (CAB) or cellulose triacetate (CTA). Adhesion of the polarizer is critical in performance, functionality and quality. U.S. Pat. No. 6,235,396 (incorporated by reference) describes an adhesive composition. A PVOH polarizer is typically treated with an adhesive agent prior to internal casting with CR39®, otherwise, no adhesion would exist.
One problem with PVOH polarized films is that they absorb water, and bubbles will result from the interaction of the moisture with the isocyanate during the casting of the poly(thio)urethane lenses, the following reactions being involved:
